Streszczenie At present, there is a growing demand of the aviation industry on the parts prepared from light alloys which are characterised with sufficient stiffness and
resistance. The technology of plastic deformation of magnesium alloys is a huge challenge. Due to the low plasticity of those materials in room temperature
the parameters of the process of plastic working must be a satisfying compromise between the cost and the quality of the products. Due to those facts,
alternative methods of plastic deformation of magnesium alloys need to be found. Particularly promising results in terms of the improvement in the susceptibility
to plastic deformation are brought by new ultra-light magnesium alloys containing lithium. With the introduction of lithium, the density of which
is 0.535 g/cm3, into the chemical composition of alloy, a further decrease of weight of alloy is achieved but at the same time the resistance of the material
decreases. The article presents the results of tests of plastic deformation of Mg–Li–RE magnesium alloys. Alloys for extrusion process were achieved with
the method of vacuum melting and casting to graphite moulds. The materials for tests were cast slabs from magnesium alloys with symbols LAE442. Before
the process of deformation the castings were subject to homogenization. The tests of extrusion were conducted in complex state of deformation with using
KOBO method. An assessment was performed of the influence of deformation process parameters on the microstructure of tested alloy. An analysis of
microstructure was conducted both in initial condition and condition after plastic deformation with the use of techniques of light and scanning transmission
electron microscopy.Słowa kluczowe: magnesium Mg-Li-RE alloy, KoBo SPD method, microstructure, electron microscopy.Abstract Obecnie obserwuje się rosnące zapotrzebowanie przemysłu lotniczego
na części wykonane ze stopów magnezu, które spełnią określone
wymagania wytrzymałościowe. Jednak mała plastyczność
stopów magnezu w temperaturze pokojowej powoduje, że są poszukiwane
alternatywne sposoby kształtowania tej grupy materiałów.
Szczególnie obiecujące w zakresie poprawy podatności do kształtowania
plastycznego są nowe ultralekkie stopy magnezu zawierające
w swoim składzie chemicznym lit. W artykule przedstawiono wyniki
analizy mikrostruktury prętów otrzymanych ze stopu LAE442 po
procesie odkształcenia metodą KoBo. Określono zmiany powstałe
w mikrostrukturze stopu LAE442 po odkształceniu plastycznym
metodą KoBo.Keywords: stopy magnezu Mg-Li-RE, metoda SPD KoBo, mikrostruktura, mikroskopia elektronowa.
1. INTRODUCTION
The basic criterion for application of modern construction materials
is their high endurance value which is expressed as the ratio of tensile
strength to density of a given material. The application of magnesium
alloys as construction elements applied in manufacturing of
means of transport led to conduction of various intensive research
operations on those materials [1, 2]. It is mainly connected with the
search for a material which will decrease the weight of the vehicle
and replace the materials which have been applied so far. Since the
1950s the interest in magnesium alloys for construction elements
has grown significantly. Magnesium alloys started to be used mainly
in aviation, car and biomedical industries. At present, there are
a lot of tests carried out on manufacturing semi-products from magnesium
alloys with the use of processes of plastic working. Besides
the conventional magnesium alloys from group Mg-Al-Zn (AZ31,
AZ80, and AZ61) and Mg-Y-RE (WE43) special attention was
turned to new generation of ultra-light alloys which include lithium
in their chemical composition. Due to the application of magnesium
as the alloying component which has density of 1.74 g/cm3, a decrease
of the weight of alloy by 30% can be achieved. Additionally,
the increase of susceptibility to plastic shaping of magnesium alloys
may be achieved by the addition of lithium in the amount of up to
15% of the alloy weight [3÷6]. Due to a big application potential
the magnesium alloys with lithium after plastic working are currently
being intensively tested. It should be mentioned here that the
disadvantage of the alloys which include lithium in their chemical
composition is the decrease of their strength and the decrease of
corrosion resistance particularly in case of high amount of this element
in the alloy and with its high reactivity [6]. Scientific research
which is conducted on this group of materials not only needed a big
amoun
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INNE PUBLIKACJE W TYM ZESZYCIE

1. INTRODUCTION
There are several types of joints that are currently applied in aerostructures.
One type is the adhesive joint, where the bonding medium
is an adhesive of special properties. Other widely applied joints
include mechanical joints, predominantly riveted [1÷3] or bolted
joints [4].
Riveted joints have been extensively used in the aircraft industry
since the emergence of first metal structures [5]. A modern aircraft
will be assembled with anywhere from several thousand to several
million rivets (e.g. Lockheed C-5 Galaxy), which are primarily used
to join thin-walled elements of lift-generating aerostructures, whose
thickness may range between several tenths to several millimeters
[6]. Despite the immense evolution of materials used in aerostructures,
commenced by the introduction of steel, through light alloys
to structural composites (laminates [7]), riveted joints still appear to
remain the most widespread joining technique [8].
The other major joining alternative present in aircraft structures
is adhesive joining. In recent years the method has been attracting
considerable attention [9÷12], particularly in the aircraft industry.
What has been long known about adhesive joining is that proper
surface treatment is critical to preparing the surface of adherends
for joining [9]. Moreover, adhesive joint formation also depends
on the suitability of a selected adhesive composition for purpose
requirements. Adhesive joining technology is undergoing a constant
and rapid development as a result of advances in the chemistry
of adhesives. Recent trends show that formerly metal elements
are often replaced with composite materials, which are lighter and
yet offer equal or even higher strength. Not only do modern composite
materials produce individual components of aircrafts, but the
whole flying objects as well (e.g. passenger planes) where the total
mass of structural composite elements exceeds 50% [12, 13]. Despite
the num więcej »

1. INTRODUCTION
Ti-2.5Cu is the most common alloy of titanium and copper. It is
characterised by very high plasticity, and is used to manufacture of
products complex shape using cold and hot plastic working. Important
properties that influence its application are also good weldability
and possibility to work at temperature up to 350°C. It has primarily
found applications in chemical apparatus and parts of automobile
and aircraft structures (e.g. in jet airliner Concorde, combat
aircraft Tornado and Jaguar) [1÷5]. As it can be seen in the Ti-Cu
phase diagram, titanium and copper may form solid solutions and
a number of intermetallics: Ti2Cu, TiCu, Ti2Cu3, TiCu3. The maximum
solubility of copper in a crystalline lattice of α titanium at the
eutectic temperature (798°C) is 2.1 wt % , whereas at the peritectic
temperature 17 wt % [6]. The structure of the alloy at equilibrium
(after a very slow cooling from 810°C) is formed by α phase grains
and a fine lamellar eutectoid mixture (α + Ti2Cu), whose volume
fraction in the structure is approx. 10% (Fig. 1).
On the other hand, a metastable martensitic phase may be formed
in the structure during a fast cooling from the range of β phase. Due
to rather high solubility of copper in a solid solution at the eutectic
temperature and its considerable reduction along with the decrease
of temperature, alloys of titanium and copper may be strengthened
by precipitation hardening. It involves the dissolving of Ti2Cu intermetallic
at a temperature above the eutectic temperature and then its
solution heat treatment and ageing. In this respect, titanium-copper
alloys are an exception among titanium alloys because the solubility
of intermetallics in α-Ti in case of other alloying elements is very
low [7]. Recommended heat treatment for this alloy (that gives the
best combination of strength and plasticity properties) is supersaturation
in air from a temperature of slightly abov więcej »

1. INTRODUCTION
The increasing requirements for efficiency of modern jet engines
and necessity of fulfilling strict environmental policies call for new
solutions in manufacturing critical gas turbine elements. One of the
ways to meet these requirements is application of ceramic thermal
barrier coatings (TBCs). The high insulating properties of TBCs
allow increase temperature in combustion chamber and turbine to
a level exceeding maximum operating temperature of metallic components.
Conventional material for insulating layer in TBC is yttria
stabilized zirconia (8YSZ — ZrO2∙8Y2O3). In the last years extensive
research focused on developing new materials were conducted.
It is expected that the new type of ceramic coating will make it possible
to increase the turbine operating temperature above 1200°C
and maintain the top-coat material phase composition stability and
thermochemical compliance with the substrate material and the
bond-coat [1].
Selection of the new material for the outer insulating layer of
TBC is very restricted. Most important restrictions include: (1) high
melting temperature, (2) lack of phase transformations in the range
between room and operating temperature, (3) low thermal conductivity,
(4) chemical inertness in contact with the bond coat and the
TGO (thermally grown oxide), (5) possibly low coefficient of thermal
expansion mismatch with the substrate material, (6) good adhesion
to the substrate material and (7) low tendency for sintering of
the porous microstructure [2].
No information concerning a material that would meet all these
requirements has been published so far. Currently applied 8YSZ
oxide is merely a compromise between these requirements. Its main
disadvantage is a limited long term operation at 1200°C. At higher
temperature the tetragonal phase transforms to cubic and monoclinic
phase which generates unfavourable stresses and consequently
leads to cracking and degradation of the c więcej »

In the last decades one of the most intensively investigated field of
the materials science is severe plastic deformation (SPD) of metals
and their alloys. SPD processing leads to significant grain-refinement
with a grain size about several hundreds of nanometers [1÷3].
Ultrafine-grained (UFG) structures obtained by SPD techniques
revealed many attractive characteristics, such as high mechanical
strength, but also adequate plasticity [2, 4÷6]. The evolution and
the character of the ultrafine-grained structures appears as a very
important factor which influences on the mechanical and functional
properties of SPD materials. The character of the UFG structures
depends on: i) homologous temperature, ii) solid solution alloying,
iii) second phase particles, iv) value of the stacking fault energy
(SFE), and additionally v) strain path effect on structure formation
[7÷9].
The most known severe plastic deformation processing methods
such as: high pressure torsion (HPT) [10], equal channel angular
pressing (ECAP) [11], multi-directional forging (MF) [12] or
hydroextrusion (HE) [13, 14] belong to techniques with constant
strain path (frequently named as monotonic deformation techniques).
During monotonic deformation the directional features of
the microstructure have been observed in [13, 15, 16]. The grains
are especially highly elongated in the direction of metal flow. Moreover,
monotonic deformation resulted in a high fraction of high angle
boundaries (HABs) and can effectively retard the annihilation of
lattice defects [7, 17, 18].
The methods with cyclic changes in the strain path such as: cyclic
extrusion compression (CEC) [19] or KoBo [20, 21], involve
the large number of variables [22÷25]. Maybe for this reason these
processes are currently not widely widespread. Cyclic methods of
deformation lead to a lower rate of grain refinement compared to
methods without a change in strain path [26]. In cyclic methods of
deformation, the więcej »

1. INTRODUCTION
In the last decades, the developments in the technologies of carbon
materials have caused new products usable as components in composite
materials. In that group, we can find carbon fibers, glassycarbon
particles, carbon nanotubes and graphene. At first, they were
extremely expensive, but with time, they became cheaper and can
be now commercially applied. Among the carbon materials, a new
one has appeared, i.e. the glassy carbon open-celled foams (Cof),
which, so far, have found applications as a sound absorption material,
a biomaterial, a catalyst support or a thermal management material
[1÷4]. The Cof are built of cells with walls containing windows
and their geometry is commercially characterized by ppi (pores per
inch), which means that the pore size increases with a ppi decrease
[3, 5÷7]. That type of macrostructure gives the opportunity for carbon
foams to be infiltrated by liquid media and to form interpenetrating
phase composites [7÷9].
The research works focused on metal matrix composites report
that continuous carbon fibers can be infiltrated by magnesium alloys,
and magnesium matrix composites with dispersed carbon
reinforcements as short fibers, particles and nanotubes can be
processed by different powder technologies and casting methods
[10÷16]. However, the results of wettability measurements are not
unequivocal. If the equilibrium contact angle θ is less than 90°(socalled
“good wettability state"), a spontaneous infiltration of molten
magnesium into the porous fibres and open-celled preforms can be
expected. The contact angle θ between the molten magnesium and
the porous graphite as well as the vitreous carbon determined by
Shi et al. [17] by the sessile drop method at 700°C in a chamber
filled with argon and magnesium vapor was 80° and 74°, respectively.
However, the works of other authors [18÷21] showed values
higher than 90° as well as poor wettability. The contact angle estima więcej »